Various heat insulators different in structure and characteristic have been used for insulation of refrigerator, vending machine, cooling box, refrigerator truck, hot water tank, ice tank, vacuum insulating piping, molded head lining of automobiles, bath tub, and others. Recently, many vacuum heat insulators showing superior heat-insulating properties have been used in these applications. Such a vacuum heat insulator generally has a structure prepared by placing a core member in a gas-barrier external packaging member, for example, of a metal-deposited film and sealing it while making inside under reduced pressure. The heat-insulating properties, productivity, and handleability of such a vacuum heat insulator depend largely on the core member described above, and examples of the core members commonly used recently include open-cell polyurethane foams (Patent Document 1), glass fiber aggregates (Patent Documents 2 and 3) and composites of glass fiber aggregate and other thermoplastic resin (Patent Document 4).
However, the commonly-used core members for vacuum heat insulator described above still have the following problems. Core members of open-cell polyurethane foam are very superior in workability, handleability, lightness in weight, and others, but inferior in heat resistance to fibrous materials such as glass fiber.
Core members of glass fiber aggregate are very superior in heat-insulating properties without generation of out-gas (gases vaporizing form core member), but have a disadvantage in the handleability and workability of the glass fiber itself. Although there are efforts to improve handleability, for example to improve operation of inserting a core member into the external packaging member, by needle-punching a sheet of glass fiber, it was not possible to overcome the difficulties in handling and workability derived from the material itself. In particular, there still remain problems in working environment and handling, when the core member is recycled. For example, seal opening of the external packaging member during recycling results in scattering of the glass fiber aggregate core member, causing problems in handleability and workability and also in environmental load.
Core members in combination of a glass fiber aggregate and other thermoplastic fiber are improved in handling to some extent but not sufficiently. In particular, Patent Document 4 discloses a core member consisting of 80 percent by mass glass wool and 20 percent by mass polypropylene resin fiber that is processed into a matt-shaped form by a heat pressing method. However, the core member still has problems of the deterioration in workability due to the glass wool itself and the deterioration in heat-insulating properties with time due to out-gas generated from the polypropylene resin fiber. In addition, combined use of organic and inorganic fibers makes fractionation after use very difficult and thus, results in very poor recycling efficiency. Although there are some reports on composites with rock wool, pulp, or the like, similarly to the composite with a thermoplastic fiber, use of a glass fiber inevitably causes the problems of the poor handleability and workability and high environmental load inherent to the glass fiber.
Although a vacuum heat insulator made only of an organic fiber, for example of a thermoplastic fiber, may possibly be used as a core member, there is no such commercially available heat insulator because of the problem of out-gas from the organic fiber. Use of a 0.75-d polyester fiber floc as a core member was studied (Patent Document 5), but use of the fiber floc resulted in deterioration in handleability, and thus, prohibits production of practical products. It is possible to process the fiber floc into sheet for improvement in handleability, but as described above, it is difficult to use a needle-punching method when an ultra-thin fiber is used, and use of a chemical bonding method leads to generation of out-gas, causing problems of larger change and drastic deterioration in heat-insulating properties with time.
On the other hand, use of vacuum heat insulators is expanding steadily recently. A vacuum heat insulator may be used in the application for improving thermal efficiency of tanks and piping, for example, while covering a cylindrical tank of water supply equipment or a cylindrical pipe in piping facility from external surface. In such an application, the vacuum heat insulator should be deformed along the peripheral surface of the tank or pipe and bonded thereto, and thus, should have a through-hole or notched area, for example, for incorporating wiring and piping or a groove for bending. However, it was difficult to bend a conventional thick core member having a vacuum thickness of 10 mm or more after evacuation. Even if it was possible to deform a core member easily before evacuation, it was difficult to produce a vacuum heat insulator by using the deformed core member.
It may be possible to make the post-evacuation deformation easier, by reducing the thickness of the core member after evacuation, for example, to 5 mm or less. However, when a glass fiber having an average fiber length of 1 mm or less was used as a core member, reduction in thickness resulted in insufficient curved-surface processability. Even if the vacuum heat insulator obtained may be easily deformed, the vacuum heat insulator could not be used easily for wrapping and lead to insufficient adhesion if used, because it tends to go back to its original flat plate shape and leave relatively large cockles generated when it is bent.
For forming a through-hole area or a notched area in a vacuum heat insulator, reported is a method of placing a flat plate-shaped insulating core member having a through-hole and/or a notch into a bag of a gas-barrier packaging material through its opening, evacuating the bag to a desirable vacuum, and forming a sealed region along the internal peripheral area in the vacuum heat insulator side of the through-hole area and/or the notched area by sealing the gas-barrier packaging materials therein to each other and a sealed region in the opening area by sealing the gas-barrier packaging materials therein to each other by contact of a heating unit under (Patent Document 6).
However, if a hard core member such as open-cell resin foam or inorganic powder is used, when the external covering material (external packaging member) in the internal peripheral area of the through-hole area or the notched area is evacuated or the cover material is sealed, a large load is applied to the internal peripheral area and causes fracture of the covering material and significant separation of the covering material from the core member, although such a phenomenon depends on the flexibility or the kind of the covering material used. A similar problem arises when multiple core members are placed in an external packaging member and the rear faces of the external packaging member are sealed to each other along the periphery of the external packaging member and the external periphery of the core members. Problems often arise in the regions particularly between multiple core members in the evacuation step.
It may be possible to smoothen the surface of the core member and thus to raise the adhesiveness between the covering material and the core member, but it demands an additional chamfering of the core member, which leads to decrease in productivity. It is even difficult to smoothen the surface of the core member, especially if it is an inorganic material.
Each of the vacuum heat insulators above is prepared by placing a core member directly in an external packaging member, making the external packaging member evacuated inside, and sealing the opening of the external packaging member, but the method raised a problem in productivity of the vacuum heat insulator. Specifically, when a core member is placed directly in an external packaging member, the external packaging member often suffers scratches, resulting in decrease in the yield of vacuum heat insulator. Also when a core member is placed directly in an external packaging member, the core member easily adheres to the finally-sealed opening in the external packaging member, for example electrostatically, tightly to the extent that the deposited core member cannot be removed sufficiently, and thus, sealing of the opening results in formation of an air vent derived from the deposited core member interconnecting inside and outside of the external packaging member and thus in decrease in the yield of vacuum heat insulator. Such a problem of decrease in yield was particularly distinctive, when a difficult-to-handle fiber floc was used as a core member. In addition, when a core member of fiber floc is placed directly in an external packaging member, the filling operation is restricted for prevention of the scratches on the external packaging member as described above, and thus, it was difficult to fill the core member to a uniform thickness, which lead to decrease in heat-insulating properties.    Patent Document 1: Japanese Unexamined Patent Publication No. 6-213561    Patent Document 2: Japanese Unexamined Patent Publication No. 8-28776    Patent Document 3: Japanese Unexamined Patent Publication No. 9-4785    Patent Document 4: Japanese Unexamined Patent Publication No. 2003-155651    Patent Document 5: Japanese Unexamined Patent Publication No. 2002-188791    Patent Document 6: Japanese Unexamined Patent Publication No. 08-303686